1. Field of the Invention
The present invention relates to a positive resist composition for use in the apparatus of producing a semiconductor such as IC, in the production of a circuit board for liquid crystal, thermal head and the like, or in other photofabrication processes, and a pattern forming method using the same. More specifically, the present invention relates to a positive resist composition suitable for the fine processing of a semiconductor device, where a light energy ray at a short wavelength such as far ultraviolet ray, X-ray and electron beam is used, and a pattern forming method using the same. In particular, the present invention relates to a positive resist composition suitably used for the fine processing of a semiconductor device, where an ArF excimer laser is used, and a pattern forming method using the same.
2. Background Art
With recent progress to a higher integration of a semiconductor integrated circuit, LSI or VLSI has come to be used in practice and at the same time, the minimum pattern width of the integrated circuit has reached the region of a sub-half micron. Thus, the processing is proceeding to finer processing.
To cope with this trend, requirements for the photolithographic technology used to form a fine pattern have become severer and severer. One known technique for attaining a fine pattern is to shorten the wavelength of exposure light used at the pattern formation of a resist.
For example, in the production of DRAM having an integration degree up to 64 M bits, the i-line (365 nm) of a high-pressure mercury lamp has been used as the light source until today. Also, in the mass production process of a 256 M-bit DRAM, a KrF excimer laser (248 nm) is practically used as the light source in place of the i-line. Furthermore, for the purpose of producing DRAM having an integration degree of 1 G bits or more, studies have been made on use of a light source having a further shorter wavelength, that is, an ArF excimer laser (193 nm), an F2 excimer laser (157 nm), an X-ray or an electron beam.
In particular, an ArF excimer laser is estimated as the exposure technique in the next generation, and development of a high-sensitivity and high-resolution resist for an ArF excimer laser is being demanded.
With respect to the resist used for the pattern formation by a lithography in this wavelength region, a chemical amplification-type resist is known. In the chemical amplification-type resist, a compound capable of generating an acid resulting from photodecomposition is generally combined with a binder resin. This binder resin is a resin having, within the molecule, a group capable of decomposing under the action of an acid to increase the solubility in an alkali developer. In addition to the above-described compound, a low molecular compound having a specific structure is sometimes blended in the chemical amplification-type resist.
In the lithography using a chemical amplification-type resist, a resist excellent in various properties such as sensitivity, resolving power, profile, coatability, heat resistance, dry etching resistance, adhesive property, substrate dependency, stability against environment (for example, dimensional stability of resist against fluctuation in the setting time) and focus depth (for example, pattern forming property with a focus gap at the irradiation of radiation), is demanded and many devices for improving the performance by additives have been hitherto disclosed.
The problem standing in the way of recent movement to refinement and high throughput is the line edge roughness. The line edge roughness means that the edge of the interface between the resist line pattern and the substrate irregularly fluctuates in the direction perpendicular to the line direction due to properties of the resist and when the pattern is observed from right above, the edge gives a rough appearance. This roughness inhibits the resolution of the pattern or is transferred by the etching step using the resist as a mask to cause deterioration of the electric characteristics and in turn reduction in the yield. Furthermore, the recent refinement requires a strict aspect ratio for the film thickness and therefore, the pattern falls down very easily. This tendency is particularly prominent in the resist for ArF. The pattern falling as used herein includes all fallings such as falling due to insufficient adhesion and falling due to insufficient film strength. In addition, the problem of development defect is serious. With respect to the resist composition for an ArF light source, a resin having introduced thereinto an alicyclic hydrocarbon moiety for imparting dry etching resistance has been proposed, but the introduction of an alicyclic hydrocarbon moiety raises a problem that the system becomes significantly hydrophobic. As a result, development with a tetramethylammonium hydroxide (hereinafter referred to as “TMAH”) which has been heretofore widely used as the developer for resist, becomes difficult or a phenomenon such as separation of the resist from the substrate during development is observed. The approach generally taken to solve the problem of pattern falling or development defect is to introduce a hydrophilic group and thereby compensate for the effect of the hydrophobic part of the resin, specifically, the alicyclic hydrocarbon moiety. However, this causes deterioration of dry etching resistance in many cases and moreover, the resist undergoes significant film loss, giving rise to a problem such as increase of light edge roughness.
For the purpose of improving the line edge roughness, pattern falling and development defect, attempts are being made to add various compounds, particularly, a non-aromatic organic low molecular compound having a hydroxyl group or a carboxyl group, to the chemical amplification resist composition. For example, for the purpose of preventing the pattern falling and improving the line edge roughness, Patent Document 1 (JP-A-2003-270791 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)) discloses a positive resist composition comprising a chain low molecular compound having at least three hydroxyl groups or substituted hydroxyl groups. Also, Patent Document 2 (JP-A-2001-343750) discloses that specific cyclohexanols are effective for the improvement of line edge roughness. As for the reduction in the development defect, Patent Document 3 (JP-A-2000-187327), Patent Document 4 (JP-A-11-338150), Patent Document 5 (JP-A-2000-47385) and Patent Document 6 (JP-A-2002-72481) disclose that addition of a low molecular compound containing a hydrophilic functional group and a cyclic hydrocarbon group is effective.
When the conventional organic low molecular compounds are used, this is surely effective for individual problems of line edge roughness, pattern falling and development defect, but it has been impossible to solve all of these problems at the same time either by using one of those organic low molecular compounds alone or by using a plurality thereof.